Cationic, advanced epoxy resin compositions from (1) diglycidyl ethers of phenols (2) diglycidyl ethers of alkane diols and (3) dihydric phenols

ABSTRACT

A method for preparing an advanced epoxy cationic resin from an epoxy-based resin containing oxirane groups by converting at least some of the oxirane groups to cationic groups, wherein the improvement is using as the epoxy-based resin an advanced epoxy resin obtained by reacting in the presence of a suitable catalyst (1) a diglycidylether of an aliphatic diol which is essentially free of ether oxygen atoms, such as a diglycidyl ether of 1,4-butanediol, (2) a digylcidylether of a dihydric phenol, for example a diglycidyl ether of bisphenol A and (3) a dihydric phenol such as bisphenol A and optionally a capping agent such as p-nonylphenol. 
     Coating compositions suitable for electrodeposition are prepared from the product obtained by the process.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of application Ser. No.07/069,459 filed July 2, 1987 now U.S. Pat. No. 4,868,230 which isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is concerned with cationic, advanced epoxy resincompositions, a method for their preparation and the use of suchcompositions in cathodic electrodeposition.

2. Description of the Prior Art

Electrodeposition has become an important method for the application ofcoatings over the last two decades and continues to grow in popularitybecause of its efficiency, uniformity and environmental acceptance.Cathodic electrodeposition has become dominant in areas where highlycorrosion-resistant coatings are required, such as in primers forautomobile bodies and parts. Epoxy based systems provide the bestoverall performance in this application and are widely used.

Cathodic electrodeposition resins based on conventional epoxies obtainedby reacting liquid diglycidyl ethers of bisphenol A with bisphenol A toproduce higher molecular weight epoxy resins have known disadvantages.Such products tend to have excessively high softening points resultingin poor flow out. In addition, such products require excessive amountsof solvent during their preparation. In order to improve flow, it hasbeen proposed to modify such conventional epoxy resins by reaction witha diol in the presence of a tertiary amine catalyst. Thus, Bosso et al.,U.S. Pat. No. 3,839,252, describes modification with polypropyleneglycol. Marchetti et al., U.S. Pat. No. 3,947,339, teaches modificationwith polyesterdiols or polytetramethylene glycols. Wismer et al., U.S.Pat. No. 4,419,467, describes still another modification with diolsderived from cyclic polyols reacted with ethylene oxide. These variousmodifications, however, also have disadvantages. Tertiary amines orstrong bases are required to effect the reaction between the primaryalcohols and the epoxy groups involved. Since these reactions requirelong cook times, they are subject to gellation because of competitivepolymerization of the epoxy groups by the base catalyst. In additionepoxy resins containing low levels of chlorine are required to preventdeactivation of this catalyst.

Many coating formulations applied by electrodeposition include pigmentsto provide color, or opacity or application or film properties. U.S.Pat. No. 3,936,405, Sturni et al., describes pigment grinding vehiclesespecially useful in preparing stable, aqueous pigment dispersions forwater-dispersible coating systems, particularly for application byelectrodeposition. The final electrodepositable compositions, asdescribed, contain the pigment dispersion and an ammonium or amine saltgroup solubilized cationic electrodepositable epoxy-containing vehicleresin and other ingredients typically used in electrodepositablecompositions. Among the kinds of resins used are various polyepoxidessuch as polyglycidyl ethers of polyphenols, polyglycidyl ethers ofpolyhydric alcohols and polyepoxides having oxyalkylene groups in theepoxy molecule.

The automobile industry still has needs in the areas of controlled filmthickness and lower temperature cure systems. The ability to buildthicker, uniform films which are smooth and free of defects will allowthe elimination of an intermediate layer of paint known as a primersurfacer or spray primer, previously required to yield a sufficientlysmooth surface for the topcoat. Such an elimination results in removalof one paint cycle and provides more efficient operations. Thickerelectrocoat primers may also provide improved corrosion resistance.

SUMMARY OF THE INVENTION

The present invention is directed to an advanced epoxy cationic resinhaving a charge density of from about 0.2 to about 0.6 milliequivalentof cationic charge per gram of resin prepared by reacting in thepresence of a suitable catalyst

(A) a composition comprising (1) at least one diglycidyl ether of analiphatic diol which diol is essentially free of ether oxygen atoms and(2) at least one diglycidyl ether of a dihydric phenol with

(B) at least one dihydric phenol and optionally,

(C) a monofunctional capping agent; wherein components (A-1) and (A-2)are employed in quantities such that from about 10 to about 75 weightpercent of the diglycidyl ethers contained in component (A) arecontributed by Component (A-1) and from 25 to about 90, weight percentof such glycidyl ethers are contributed by component (A-2) andcomponents (A) and (B) are employed in such quantities that theresultant advanced epoxy resin has an average epoxide equivalent weightof from about 350 to about 10,000, whereby there is formed an advancedepoxy resin having terminal oxirane groups; and

subsequently converting the oxirane groups to cationic groups byreacting the resin with a nucleophile and adding an organic acid andwater at at least one point in the process.

The present invention is also directed to a coating compositioncomprising an aqueous dispersion of the above-described cationic,advanced epoxy resin, a method for making such compositions and a methodfor coating such compositions.

DETAILED DESCRIPTION OF THE INVENTION

The cationic, advanced epoxy resin compositions of the invention containthe resins obtained from a selected advanced epoxy resin having terminaloxirane groups by reacting at least some of the epoxy (oxirane) groupsof the resin with a nucleophile and adding an organic acid and water atsome point during the preparation.

The Advanced Epoxy Resin

The starting epoxy resin component for preparing the cationic, advancedepoxy resin compositions is an advanced resin prepared by reacting acomposition comprising a glycidyl ether of an aliphatic diol which diolis essentially free of ether oxygen atoms (A-1), a glycidyl ether of adihydric phenol (A-2) with a dihydric phenol (B) and optionally, amonohydric capping agent (C). Glycidyl ethers of dihydric phenols usefulfor the preparation of these resins are those having at least one, andpreferably an average of about two, vicinal epoxide groups per molecule.These polyepoxides can be produced by condensation of an epihalohydrinwith a polyphenol in the presence of a basic acting substance.

Useful glycidyl ethers of polyphenols are represented by Formulae I andII: ##STR1## wherein A is a divalent hydrocarbon group having from 1 to12, preferably 1 to 6 carbon atoms, --S--, --S--S--, --SO--, --SO₂ --,--CO--, --O--CO--O--, --O-- or the like; each R is independentlyhydrogen or a hydrocarbyl group having from 1 to 3 carbon atoms; each R'is independently hydrogen, a hydrocarbyl or hydrocarbyloxy group havingfrom 1 to 4 carbon atoms, or a halogen, preferably chlorine or bromine;n has a value from zero to 1; and n' has a value from zero to about 10,preferably from 0.1 to 5.

Polyphenols useful for the production of these polyepoxides include2,2-bis(4-hydroxyphenyl)propane (bisphenol A),1,1-bis(4-hydroxyphenyl)ethane, bis(4-hydroxyphenyl)methane (bisphenolF), p,p'-hydroxybiphenol, resorcinol, hydroquinone, or the like. Theparticularly preferred polyglycidyl ethers of polyphenols are thediglycidyl ether of bisphenol A and the oligomeric polyglycidyl ethersof bisphenol A.

The glycidyl ethers of aliphatic diols essentially free of ether oxygenatoms useful in preparation of these epoxy resins are those having thestructure: ##STR2## wherein each R is independently hydrogen or ahydrocarbyl group having from 1 to 3 carbon atoms; Z is a divalentaliphatic or cycloaliphatic group essentially free of ether oxygen atomsand having from 2 to about 20, preferably from 2 to about 12, carbonatoms or one of the groups represented by the formulas ##STR3## A' is adivalent hydrocarbon group having from 1 to about 6 carbon atoms; eachR' is independently hydrogen, a hydrocarbyl or hydrocarbyloxy grouphaving from 1 to 4 carbon atoms; each R" is an aliphatic group havingfrom 1 to about 6, preferably from 1 to about 4, carbon atoms; and n hasa value of zero or 1. Examples of useful aliphatic diols which areessentially free of ether oxygen atoms are 1,4-butanediol,1,6-hexanediol, 1,12-dodecanediol, neopentylglycol, dibromoneopentylglycol, 1,3-cyclohexanediol, hydrogenated bisphenol A,1,4-cyclohexanedimethanol, 1,2-cyclohexanediol, 1,4-cyclohexanediol,combinations thereof and the like.

The glycidyl ethers of aliphatic diols which are essentially free ofether oxygen atoms can be produced by the condensation of anepihalohydrin with an aliphatic diol which is essentially free of etheroxygen atoms having the structure:

    HO--Z--OH

where Z is as defined above. The resultant halohydrin ether product isthen dehydrohalogenated by known methods with a basic acting materialsuch as sodium hydroxide.

Some of the common methods of synthesis of the diglycidylethers ofaliphatic diols which are essentially free of ether oxygen atoms producesignificant amounts of organic chloride-containing impurities. However,other processes are known for preparing products with lower levels ofsuch impurities. While the low-chloride resins are not required for thepractice of this invention, they may be used, if desired, for possibleimprovements in the process of preparing the resins, in the storageproperties of the resins or formulated coatings made therefrom or in theperformance properties of the products.

Mixtures containing the above two glycidyl ether components are reactedwith a diphenol and, optionally, a capping agent to produceepoxy-functional resins having the desired epoxide (oxirane) groupcontent which are used to prepare the resins of the invention. Theeffective proportions of the diglycidyl ether components range fromabout 10 to about 75 weight percent of the diglycidylether of analiphatic diol essentially free of ether oxygen atoms (A-1) and fromabout 25 to about 90 weight percent of the diglycidyl ether of adiphenol (A-2). However, better overall results are obtained with fromabout 10 to about 50 weight percent of the diglycidylether of analiphatic diol essentially free of ether oxygen atoms and from about 50to about 90 weight percent of the diglycidylether of a phenol.Especially preferred is from about 15 to about 35 weight percent of thediglycidylether of an aliphatic diol essentially free of ether oxygenatoms and correspondingly from about 65 to about 85 weight percent ofthe diglycidyl ether of a diphenol. While products containing higherthan 90 percent of the diglycidylether of an aliphatic diol essentiallyfree of ether oxygen atoms will electrodeposit to give high film build,their rupture voltage limits their use to the lower voltages which donot provide sufficient throwing power for many applications such as inelectrocoating automobile bodies. The proportions of the glycidyl ethercomponents (A=A-1+A-2) and the dihydric phenol (B) are selected toprovide an average epoxy equivalent weight in the advanced epoxy resinof from about 350 to about 10,000, preferably from about 600 to about3,000. Such proportions usually are in the range of from about 60 toabout 90 weight percent of A and from about 10 to about 40 weightpercent of B. Useful diphenolic compounds include those described aboveas suitable for production of polyepoxide. The preferred diphenol isbisphenol A. Also useful are the bisphenols produced by chain extensionof the diglycidyl ether of a bisphenol with a molar excess of abisphenol to produce a diphenolic functional oligomeric product.

The use of capping agents such as monofunctional phenolic compoundsprovides the advantageous ability to reduce the epoxide content of theresulting product without chain-extension reactions and thus allowsindependent control of the average molecular weight and the epoxidecontent of the resulting resin within certain limits. Use of amonofunctional compound to terminate a certain portion of the resinchain ends also reduces the average epoxy functionality of the reactionproduct. The monofunctional phenolic compound is typically used atlevels of zero to 0.7 equivalent of phenolic hydroxyl groups perequivalent of epoxy which would remain after reaction of substantiallyall of the phenolic groups of the diphenol.

Examples of useful monofunctional capping agents are monofunctionalphenolic compounds such as phenol, tertiary-butyl phenol, cresol,para-nonyl phenol, higher alkyl substituted phenols, and the like.Particularly preferred is para-nonyl phenol. The total number ofphenolic groups and the ratio of difunctional to monofunctional phenoliccompounds, if any are used, are chosen so that there will be astoichiometric excess of epoxide groups. Ratios are also chosen so thatthe resulting product will contain the desired concentration of terminalepoxy groups and the desired concentration of resin chain endsterminated by the monophenolic compound after substantially all of thephenolic groups are consumed by reaction with epoxy groups. Usually, theamount of the capping agent is from about 1 percent to about 15 percentbased on the total weight of the A and B components.

These amounts are dependent on the respective equivalent weights of thereactants and the relative amounts of the epoxy-functional componentsand may be calculated by methods known in the art. In the practice ofthis invention, the desired epoxide content of the reaction productuseful for preparation of the cationic resin is typically between 1 and5 percent, calculated as the weight percentage of oxirane groups, andpreferably is from about 2 to about 4 percent. These levels arepreferred because they provide, after conversion, the desired cationiccharge density in the resinous products useful in cathodicelectrodeposition. These cationic resins are produced by conversion ofpart or all of the epoxy groups to cationic groups as described below.

Reaction of the monofunctional compound with epoxy groups of thepolyglycidylether components of the reaction mixture may be done priorto, substantially simultaneously with, or subsequent to thechain-extension reactions of the diphenolic compound and thepolyglycidylether components. The preferred method is to have all of thereactants present simultaneously.

Reactions of the above components to produce the epoxy resins aretypically conducted by mixing the components and heating, usually in thepresence of a suitable catalyst, to temperatures between 130° and 200°C., preferably between 150° and 175° C., until the desired epoxidecontent of the product is reached. The reaction optionally may beconducted in an appropriate solvent to reduce the viscosity, facilitatemixing and handling, and assist in controlling the heat of reaction.

Many useful catalysts for the desired reactions are known in the art.Examples of suitable catalysts include ethyltriphenylphosphoniumacetate.acetic acid complex, ethyltriphenylphosphonium chloride,ethyltriphenylphosphonium bromide, ethyltriphenylphosphonium iodide, orethyltriphenylphosphonium phosphate, and tetrabutylphosphoniumacetate.acetic acid complex. The catalysts are typically used at levelsof 0.01 to 0.5 mole percent of the epoxide groups.

Appropriate solvents include aromatic solvents, glycol ethers, glycolether esters, high boiling esters or ketones, or mixtures. Other usefulsolvents will be apparent to those skilled in the art. Preferredsolvents are ethylene glycol monobutylether and propylene glycolmonophenylether. Solvent content may range from zero to about 30 percentof the reaction mixture. A solvent is usually chosen which is compatiblewith the subsequent cation-forming reactions and with the final coatingcomposition so that the solvent does not require subsequent removal.

Unexpectedly, incorporation of these glycidyl ethers of aliphatic diolsessentially free of ether oxygen atoms into the epoxy resin confer tocathodically electrodepositable coating compositions produced therefromthe ability to build thicker films having controlled thickness duringthe electrodeposition process, as compared to a similar compositionusing an epoxy resin not containing the aliphatic diol essentially freeof ether oxygen atoms/glycidyl ether component. The ability to depositthicker films is highly desirable for reducing the number of paintapplications required while improving the corrosion resistance andappearance of the electrodeposited coating. The film thickness can becontrolled by adjusting the amount of the diglycidylether of aliphaticdiol essentially free of ether oxygen atoms incorporated into the epoxyresin. Generally, thickness increases with increasing content of thiscomponent.

Another advantage is that the cationic epoxy resins containing thediglycidylether of an aliphatic diol essentially free of ether oxygenatoms have a lower viscosity at a given temperature than unmodifiedcationic resins of the same molecular weight. This lower viscosityallows the use of higher molecular weight resins and/or less solvent toachieve a viscosity comparable to an unmodified resin. The lowerviscosity resins allow the coating composition greater flowout duringdeposition and curing which results in better appearance. Alternatively,the lower viscosity resins enable curing at lower temperatures to giveequivalent flow and appearance. Finally, coatings produced using theseepoxy resins have greater flexibility due to incorporation of thediglycidylether of an aliphatic diol essentially free of ether oxygenatoms component as compared to those based on similar resins notcontaining that component.

The Nucleophile

The nucleophilic compounds which can be used advantageously in formingthe cations required by this invention are represented by the followingclasses of compounds, sometimes called Lewis bases:

(a) monobasic heteroaromatic nitrogen compounds;

(b) tetra (lower alkyl)thioureas;

(c) R¹ --S--R² wherein R¹ and R² individually are lower alkyl, hydroxylower alkyl or wherein R¹ and R² are combined as one alkylene radicalhaving 3 to 5 carbon atoms;

(d) ##STR4## wherein R³ and R⁴ individually are lower alkyl, hydroxylower alkyl, ##STR5## or are combined as one alkylene radical havingfrom 3 to 5 carbon atoms, R⁶ is an alkylene group having from 2 to 10carbon atoms, R⁷ and R⁸ individually are lower alkyl and R⁵ is hydrogenor lower alkyl, aralkyl or aryl, except that when R³ and R⁴ together arean alkylene group then R⁵ is hydrogen, lower alkyl or hydroxyalkyl andwhen either or both of R³ and R⁴ is ##STR6## then R⁵ is hydrogen; and(e) ##STR7## wherein R⁹, R¹⁰ and R¹¹ individually are lower alkyl,hydroxy lower alkyl or aryl.

In this specification the term lower alkyl means an alkyl having from 1to 6 carbon atoms such as methyl, ethyl, propyl, isopropyl, n-butyl,isobutyl, n-pentyl, isopentyl, n-hexyl and isohexyl.

Representative specific nucleophilic compounds are pyridine,nicotinamide, quinoline, isoquinoline, tetramethyl thiourea, tetraethylthiourea, hydroxyethyl methyl sulfide, hydroxyethyl ethyl sulfide,dimethyl sulfide, diethyl sulfide, di-n-propyl sulfide, methyl-n-propylsulfide, methylbutyl sulfide, dibutyl sulfide, dihydroxyethyl sulfide,bis-hydroxybutyl sulfide, trimethylene sulfide, thiacyclohexane,tetrahydrothiophene, dimethylamine, diethylamine, dibutylamine,N-methylethanolamine, diethanolamine and the ketimine derivatives ofpolyamines containing secondary and primary amino groups such as thoseproduced by the reaction of diethylene triamine orN-aminoethylpiperazine with acetone, methyl ethyl ketone ormethylisobutyl ketone; N-methylpiperidine, N-ethylpyrrolidine,N-hydroxyethylpyrrolidine, trimethylphosphine, triethylphosphine,tri-n-butylphosphine, trimethylamine, triethylamine, tri-n-propylamine,triisobutylamine, hydroxyethyldimethylamine, butyldimethylamine,trihydroxyethylamine, triphenylphosphine, andN,N,N-dimethylphenethylamine.

The Acid

Substantially any organic acid, especially a carboxylic acid, can beused in the conversion reaction to form onium salts so long as the acidis sufficiently strong to promote the reaction between the nucleophileand the vicinal epoxide group(s) on the resinous reactant. In the caseof the salts formed by addition of acid to a secondary amine/epoxy resinreaction product, the acid should be sufficiently strong to protonatethe resultant tertiary amine product to the extent desired.

Monobasic acids are normally preferred (H.sup.⊕ A.sup.⊖). Suitableorganic acids include, for example, alkanoic acids having from 1 to 4carbon atoms (e.g., acetic acid, propionic acid, etc.), alkenoic acidshaving up to 5 carbon atoms (e.g., acrylic acid, methacrylic acid, etc.)hydroxy-functional carboxylic acids (e.g., glycolic acid, lactic acid,etc.) and organic sulfonic acids (e.g., methanesulfonic acid), and thelike. Presently preferred acids are lower alkanoic acids of 1 to 4carbon atoms with lactic acid and acetic acid being most preferred. Theanion can be exchanged, of course, by conventional anion exchangetechniques. See, for example, U.S. Pat. No. 3,959,106 at column 19.Suitable anions are chloride, bromide, bisulfate, bicarbonate, nitrate,dihydrogen phosphate, lactate and alkanoates of 1-4 carbon atoms.Acetate and lactate are the most preferred anions.

The Conversion Process to Form Cationic Resins

The conversion reaction is normally conducted by merely blending thereactants together and maintaining the reaction mixture at an elevatedtemperature until the reaction is complete or substantially complete.The progress of the reaction is easily monitored. The reaction isnormally conducted with stirring and is normally conducted under anatmosphere of inert gas (e.g., nitrogen). Satisfactory reaction ratesoccur at temperatures of from about 25° C. to about 100° C., withpreferred reaction rates being observed at temperatures from about 60°to about 80° C.

Good results can be achieved by using substantially stoichiometricamounts of reactants although a slight excess or deficiency of the epoxycontaining resin or the nucleophile can be used. With weak acids, usefulratios of the reactants range from 0.5 to 1.0 equivalent of nucleophileper epoxide group of the resin and 0.6 to 1.1 equivalents of acid perepoxide. These ratios, when combined with the preferred epoxide contentresins described above, provide the desired range of cationic chargedensity required to produce a stable dispersion of the coatingcomposition in water. With still weaker acids (e.g., a carboxylic acid,such as acetic acid) a slight excess of acid is preferred to maximizethe yield of onium salts. In preparing the compositions in which thecationic group being formed is an onium group, the acid should bepresent during the reaction of the nucleophile and the epoxy group ofthe resin. When the nucleophile is a secondary amine, the amine-epoxyreaction can be conducted first, followed by addition of the acid toform the salt and thus produce the cationic form of the resin.

For the onium-forming reactions, the amount of water that is alsoincluded in the reaction mixture can be varied to convenience so long asthere is sufficient acid and water present to stabilize the cationicsalt formed during the course of the reaction. Normally, it has beenfound preferable to include water in the reaction in amounts of fromabout 5 to about 30 moles per epoxy equivalent. When the nucleophile isa secondary amine, the water can be added before, during, or after theresin epoxy group/nucleophile reaction. The preferred range of chargedensity of the cationic, advanced epoxy resin is from about 0.2 to about0.6 milliequivalent of charge per gram of the resin.

It has also been found advantageous to include minor amounts ofwater-compatible organic solvents in the reaction mixture. The presenceof such solvents tends to facilitate contact of the reactants andthereby promote the reaction rate. In this sense, this particularreaction is not unlike many other chemical reactions and the use of suchsolvent modifiers is conventional. The skilled artisan will, therefore,be aware of which organic solvents can be included. One class ofsolvents that we have found particularly beneficial are the monoalkylethers of the C₂ -C₄ alkylene glycols. This class of compounds includes,for example, the monomethyl ether of ethylene glycol, the monobutylether of ethylene glycol, etc. A variety of these alkyl ethers ofalkylene glycols are commercially available.

When a desired degree of reaction is reached, any excess nucleophile canbe removed by standard methods, e.g., dialysis, vacuum stripping andsteam distillation.

Other Embodiments of the Invention

The cationic, advanced epoxy resins of this invention in the form ofaqueous dispersions are useful as coating compositions, especially whenapplied by electrodeposition. The coating compositions containing thecationic resins of this invention as the sole resinous component areuseful but it is preferred to include crosslinking agents in the coatingcomposition so that the coated films, when cured at elevatedtemperatures, will be crosslinked and exhibit improved film properties.The most useful sites on the resin for crosslinking reactions are thesecondary hydroxyl groups along the resin backbone. Materials suitablefor use as crosslinking agents are those known to react with hydroxylgroups and include, for example, blocked polyisocyanates; amine-aldehyderesins such as melamine-formaldehyde, urea-formaldehyde,benzoguanine-formaldehyde, and their alkylated analogs; andphenol-aldehyde resins.

Particularly useful and preferred crosslinking agents are the blockedpolyisocyanates which, at elevated temperatures, deblock and formisocyanate groups which react with the hydroxyl groups of the resin tocrosslink the coating. Such crosslinkers are typically prepared byreaction of the polyisocyanate with a monofunctional active-hydrogencompound.

Examples of polyisocyanates suitable for preparation of the crosslinkingagent are described in U.S. Pat. No. 3,959,106 to Bosso, et al., inColumn 15, lines 1-24, incorporated by reference herein. Also suitableare isocyanate-functional prepolymers derived from polyisocyanates andpolyols using excess isocyanate groups. Examples of suitable prepolymersare described by Bosso, et al., in U.S. Pat. No. 3,959,106, Column 15,lines 25-57, incorporated herein by reference. In the preparation of theprepolymers, reactant functionality, equivalent ratios, and methods ofcontacting the reactants must be chosen in accordance withconsiderations known in the art to provide ungelled products having thedesired functionality and equivalent weight.

Preferred polyisocyanates are the isocyanurate trimer of hexamethylenediisocyanate, toluene diisocyanate, methylene diphenylene diisocyanate,isophorone diisocyanate and a prepolymer of toluene diisocyanate andtrimethylolpropane.

Suitable blocking agents include alcohols, phenols, oximes, lactams, andN,N-dialkylamides or esters of alpha-hydroxyl group containingcarboxylic acids. Examples of suitable blocking agents are described inU.S. Pat. No. 3,959,106 to Bosso, et al., in Column 15, line 58, throughColumn 16, line 6, and in U.S. Pat. No. 4,452,930 to Moriarity.Particularly useful are the oximes of ketones, also known as ketoximes,due to their tendency to deblock at relatively lower temperatures andprovide a coating composition which can be cured at significantly lowertemperatures. The particularly preferred ketoxime is methyl ethylketoxime.

These cationic resins of the invention, when formulated with certainpreferred ketoxime-blocked polyisocyanates, provide coating compositionswhich cure at significantly lower temperatures than those of the priorart.

The blocked polyisocyanates are prepared by reacting equivalent amountsof the isocyanate and the blocking agent in an inert atmosphere such asnitrogen at temperatures between 25° C. to 100° C., preferably below 70°C. to control the exothermic reaction. Sufficient blocking agent is usedso that the product contains no residual, free isocyanate groups. Asolvent compatible with the reactants, product, and the coatingcomposition may be used such as a ketone or an ester. A catalyst mayalso be employed such as dibutyl tin dilaurate.

The blocked polyisocyanate crosslinking agents are incorporated into thecoating composition at levels coresponding to from about 0.2 to about2.0 blocked isocyanate groups per hydroxyl group of the cationic resin.The preferred level is from about 0.5 to about 1.0 blocked isocyanategroup per resin hydroxyl group.

A catalyst optionally may be included in the coating composition toprovide faster or more complete curing of the coating. Suitablecatalysts for the various classes of crosslinking agents are known tothose skilled in the art. For the coating compositions using the blockedpolyisocyanates as crosslinking agents, suitable catalysts includedibutyl tin dilaurate, dibutyl tin diacetate, dibutyl tin oxide,stannous octanoate, and other urethane-forming catalysts known in theart. Amounts used typically range between 0.1 and 3 weight percent ofbinder solids.

Unpigmented coating compositions are prepared by blending the cationicresinous product with the crosslinking agent and optionally anyadditives such as catalysts, solvents, surfactants, flow modifiers,defoamers, or other additives. This mixture is then dispersed in waterby any of the known methods. A particularly preferred method is thetechnique known as phase-inversion emulsification, wherein water isslowly added with agitation to the above mixture, usually attemperatures ranging from ambient to 70° C., until the phases invert toform an organic phase-in-water dispersion. The solids content of theaqueous dispersion is usually between 5 and 30 percent by weight andpreferably between 10 and 25 percent by weight for application byelectrodeposition.

Pigmented coating compositions are prepared by adding a concentrateddispersion of pigments and extenders to the unpigmented coatingcompositions. This pigment dispersion is prepared by grinding thepigments together with a suitable pigment grinding vehicle in a suitablemill as known in the art.

Pigments and extenders known in the art are suitable for use in thesecoatings including pigments which increase the corrosion resistance ofthe coatings. Examples of useful pigments or extenders include titaniumdioxide, talc, clay, lead oxide, lead silicates, lead chromates, carbonblack, strontium chromate, and barium sulfate.

Pigment grinding vehicles are known in the art. A preferred pigmentgrinding vehicle for use in this invention consists of a water-solublecationic resinous product, water, and a minor amount of glycol ethersolvent. The cationic resinous product is prepared by reacting anepichlorohydrin/bisphenol A condensation product having an epoxide groupcontent of about 8 percent with a nucleophile, an acid, and water in asimilar fashion as described above for the cationic resins used in thepreferred embodiment of the invention. The water-soluble product may bediluted with water to form a clear solution useful as a pigment grindingvehicle.

The pH and/or conductivity of the coating compositions may be adjustedto desired levels by the addition of compatible acids, bases, and/orelectrolytes known in the art. Other additives such as solvents,surfactants, defoamers, anti-oxidants, bactericides, etc. may also beadded to modify or optimize properties of the compositions or thecoating in accordance with practices known to those skilled in the art.

Although the coating compositions of the invention may be applied by anyconventional technique for aqueous coatings, they are particularlyuseful for application by cathodic electrodeposition, wherein thearticle to be coated is immersed in the coating composition and made thecathode, with a suitable anode in contact with the coating composition.When sufficient voltage is applied, a film of the coating deposits onthe cathode and adheres. Voltage may range from 10 to 1,000 volts,typically 50 to 500. The film thickness achieved generally increaseswith increasing voltage. In the case of the coating compositions of theinvention, thicker films are achieved by incorporation of the diglycidylether of an aliphatic diol essentially free of ether oxygen atoms intothe epoxy resin used to produce the cationic resins of the invention.Also, control over the final thickness may be exercised by adjusting theamount of that component used. Current is allowed to flow for between afew seconds to several minutes, typically two minutes over which timethe current usually decreases. Any electrically conductive substrate maybe coated in this fashion, especially metals such as steel and aluminum.Other aspects of the electrodeposition process, such as bathmaintainence, are conventional. After deposition, the article is removedfrom the bath and typically rinsed with water to remove that coatingcomposition which does not adhere.

The uncured coating film on the article is cured by heating at elevatedtemperatures, ranging from about 200° F. to about 400° F., for periodsof about 1 to about 60 minutes. For the embodiments of the inventionusing the ketoxime-blocked polyisocyanate curing agents, satisfactorycure of the resulting coating can be achieved at cure schedules as lowas 250° F. for 30 minutes, as compared to 325° F. to 350° F. for 20 to30 minutes for systems typically used in the art.

All of the coating compositions of the invention provide usefulcathodically electrodepositable coatings having improved flowout, filmbuild, and flexibility properties due to the incorporation of thediglycidyl ether of an aliphatic diol essentially free of ether oxygenatoms component.

EXAMPLES

In the following examples, epoxy resins were used as starting materialswhich are characterized as follows:

Epoxy Resin A is the diglycidyl ether of 1,4-butanediol having anepoxide equivalent weight (EEW) of 125 available from WilmingtonChemical Corp. as Heloxy™ WC-67.

Epoxy Resin B is the diglycidyl ether of cyclohexanedimethanol having anEEW of 163 available from Wilmington Chemical Corp. as Heloxy™ MK-107.

Epoxy Resin C is the diglycidyl ether of neopentyl glycol having an EEWof 135 available from Wilmington Chemical Corporation as Heloxy™ WC-68.

Epoxy Resin D is a diglycidyl ether of bisphenol A having an EEW of 187.

Curing Agent A is a blocked polyisocyanate available from Mobay ChemicalCompany as Desmodur KL5-2540. The material is believed to be thereaction product of methyl ethyl ketoxime and a polyisocyanate which issubstantially the isocyanurate trimer of hexamethylene diisocyanate. Theproduct is supplied as a 75 percent solution of the blockedpolyisocyanate in propylene glycol monomethylether acetate.

Curing Agent B is prepared by charging to a one-liter, round-bottomflask fitted with a nitrogen inlet, thermometer, condenser, mechanicalstirrer, and an additional funnel with 626.3 parts by weight (pbw) ofSpencer Kellog's Spenkel™ P49-A6-60, a 60 percent solution of anisocyanate terminated prepolymer from toluene diisocyanate andtrimethylolpropane dissolved in methoxypropyl acetate. The solution isstirred at ambient temperature (22° C. to 24° C.) and 0.62 pbw ofdibutyl tin dilaurate catalyst is added. Two hundred pbw of2-ethylhexanol is added dropwise over a period of two hours. Thetemperature of the reaction mixture is allowed to rise, during theaddition, to 50° C. to 60° C. The reaction mixture is then cooled toambient temperature over two hours. The infrared spectrum of the productshows no residual unreacted isocyanate groups. The product solution isapproximately 68.9 percent non-volatile.

Pigment Grinding Vehicle A is prepared by charging into a two-liter,round-bottom flask fitted with a nitrogen inlet, thermometer, mechanicalstirrer and condenser 340.3 parts by weight (pbw) of Epoxy Resin D and109.7 pbw of bisphenol A. The mixture is stirred under a nitrogenatmosphere and heated to 90° C. to form a clear mixture. A solutioncontaining 70 percent by weight of ethyl triphenyl phosphoniumacetate.acetic acid complex in methanol (0.6 pbw) is added. The mixtureis then heated to 150° C. at a rate of 1° C. to 2° C. per minute andthen allowed to exotherm to 170° C. The temperature is raised to 175° C.and maintained for 30 minutes, at which time the epoxide content of theresin is 8.1 percent by weight. The resin is cooled to 130° C., dilutedwith 50.0 pbw of ethylene glycol monobutyl ether, and cooled to 75° C.to give an epoxy resin solution. A mixture of 77.5 pbw of nicotinamide,72.4 pbw of lactic acid, and 212.5 pbw of water is added to the resinsolution over 65 minutes at 73° to 79° C. The mixture is then reacted 3hours at 76° to 79° C. The resulting clear, light yellow, cationic resinsolution is diluted to approximately 40 percent non-volatiles with 673.1pbw of water to produce a clear, yellow solution useful as a pigmentgrinding vehicle.

Pigment Grinding Vehicle B is prepared by charging into a two-liter,round-bottom flask fitted with a nitrogen inlet, thermometer, mechanicalstirrer and condenser 340.3 parts by weight (pbw) of Epoxy Resin D and109.7 pbw of bisphenol A. The mixture is stirred under a nitrogenatmosphere and heated to 90° C. to form a clear mixture. A solutioncontaining 70 percent by weight of ethyl triphenyl phosphoniumacetate.acetic acid complex in methanol (0.6 pbw) is added. The mixtureis then heated to 150° C. at a rate of 1° C. to 2° C. per minute andthen allowed to exotherm to 170° C. The temperature is raised to 175° C.and maintained for 30 minutes, at which time the epoxide content of theresin is 8.1 percent by weight. The resin is cooled to 130° C., dilutedwith 50.0 pbw of ethylene glycol monobutyl ether, and cooled to roomtemperature to give an epoxy resin solution. A portion, 422 pbw, of thisadvanced epoxy resin solution is heated to 65° C. and 47.1 pbw ofN-methyl-2-aminoethanol is added dropwise over 22 minutes with coolingto maintain a temperature at 65° C. to 74° C. The temperature is thenmaintained at 80° C. for three hours. A solution, 75.4 pbw, whichcontains 75 percent of lactic acid is diluted with water and then theresulting solution is added at 75° C. to 80° C. to the reaction mixture.Thereafter, dilution of the product with additional water, 458.7 pbw,provides a cationic epoxy resin solution containing 40 percentnon-volatiles.

Pigment Paste A is prepared by placing a pigment blend, 100 pbw,comprising 35 pbw of clay, 35 pbw of titanium dioxide, 20 pbw of leadsilicate and 10 pbw of carbon black in a metal paint can along with 50pbw of Pigment Grinding Vehicle A. Enough chrome-plated steel pellets,about 2 mm in diameter by 5 mm long, are added to comprise aboutone-third of the final bulk volume. The pigments are ground anddispersed in the vehicle by placing the can on a paint shaker for 45minutes. Water is then added and blended in to reduce the viscosityslightly and the grinding pellets removed by filtration. The finalpigment dispersion contains 55 percent pigment by weight.

Pigment Paste B is prepared in the same manner as Pigment Paste A exceptthat Pigment Grinding Vehicle B is employed instead of Pigment GrindingVehicle A.

COATING AND TESTING THE COMPOSITIONS

The coating compositions are placed in a stainless steel tank, agitated,and maintained at 80° F. Unpolished steel test panels having Bonderite™40 treatment and P60 rinse available from Advanced Coating Technologies,Inc. are immersed in the tank and connected as the cathode to a D.C.voltage source, with the tank walls serving as the anode. The desiredvoltage is applied for two minutes, then the panels are removed, rinsedwith deionized water, and baked at the specified temperature for 30minutes.

EXAMPLE 1

A cationic electrodeposition resin is prepared by charging into asuitable reactor 27 grams of Epoxy Resin A, 81 grams of Epoxy Resin D,20 grams of nonyl phenol, and 72 grams of bisphenol A. The mixture isheated to 80° C. and 0.15 gram of a 70 percent by weight solution ofethyltriphenyl phosphonium acetate.acetic acid complex in methanol isadded. This blend is stirred while heating at 1.5° C./min. to 150° C.whereupon it exotherms to 165° C. where the temperature is held forabout one hour. The EEW of the resulting resin is 2028 grams/equivalent.

After cooling this resin to 120° C., 22 grams of propylene glycol phenylether solvent is added. The resin solution is cooled to 60° C. and 7.5grams of N-methylethanolamine is added whereupon it exotherms to 67° C.and the temperature is controlled at 60° C. for one hour.

To the reaction product at 60° C., are added 2.06 grams of dibutyl tindilaurate catalyst and 137.6 grams of Curing Agent A.

While agitating continuously, a cationic dispersion is prepared byadding to the resulting mixture, at 60° C., 9.82 grams of an aqueoussolution containing 75 percent by weight of lactic acid which isfollowed by the slow addition of 1401 grams of deionized water. Thisproduct is referred to as Resin Dispersion 1.

Resin Dispersion 1 is blended with 148 grams of Pigment Paste B to yielda cathodic electrodeposition paint having a pigment to binder ratio of0.2 to 1. Steel panels pretreated with zinc phosphate are cathodicallyelectrodeposited at various voltages for 2 minutes at a bath temperatureof 82° F. (27° C.). The wet films are baked at 275° F. (135° C.) for 30minutes. Film thicknesses are given in Table I.

EXAMPLE 2

A cationic electrodeposition resin is prepared by charging into asuitable reactor 27.5 grams of Epoxy Resin B, 82.5 grams of Epoxy ResinD, 20 grams of nonyl phenol, and 70 grams of bisphenol A. The mixture isheated to 80° C. and 0.11 gram of ethyltriphenyl phosphoniumacetate.acetic acid complex catalyst blended stirred while heating at1.5° C./min. to 150° C. whereupon it exotherms to 165° C. where thetemperature is held for about one hour. The EEW of the resulting resinis 1641 grams/equivalent.

After cooling this resin to 120° C., 22 grams of propylene glycol phenylether solvent is added. The resin solution is cooled to 60° C. and 9grams of N-methylethanolamine is added whereupon it exotherms to 67° C.and the temperature is controlled at 60° C. for one hour.

To the reaction product at 60° C., are added 2.09 grams of dibutyl tindilaurate catalyst and 139 grams of Curing Agent A.

While agitating continuously, a cationic dispersion is prepared byadding to the resulting mixture, at 60° C., 12.3 grams of an aqueoussolution containing 75 percent by weight of lactic acid which isfollowed by the slow addition of 1427 grams of deionized water. Thisproduct is referred to as Resin Dispersion 2.

Resin Dispersion 2 is blended with 112 grams of Pigment Paste B to yielda cathodic electrodeposition paint having a pigment to binder ratio of0.2 to 1. Steel panels pretreated with zinc phosphate are cathodicallyelectrodeposited at various voltages for 2 minutes at a bath temperatureof 82° F. (27° C.). The wet films are baked at 275° F. (135° C.) for 30minutes. Film thicknesses are given in Table I.

EXAMPLE 3

A cationic electrodeposition resin is prepared by charging into asuitable reactor 27 grams of Epoxy Resin C, 81 grams of Epoxy Resin D,20 grams of nonyl phenol, and 72 grams of bisphenol A. The mixture isheated to 80° C. and 0.11 gram of ethyltriphenyl phosphoniumacetate.acetic acid complex catalyst blended with 0.04 gram of methanolis added. This blend is stirred while heating at 1.5° C./min. to 150° C.whereupon it exotherms to 165° C. where the temperature is held forabout one hour. The EEW of the resulting resin is 2337 grams/equivalent.

After cooling this resin to 120° C., 22 grams of propylene glycol phenylether solvent is added. The resin solution is cooled to 60° C. and 6.42grams of N-methylethanolamine is added whereupon it exotherms to 67° C.and the temperature is controlled at 60° C. for one hour.

To the reaction product at 60° C., are added 2.06 grams of dibutyl tindilaurate catalyst and 138 grams of Curing Agent A.

While agitating continuously, a cationic dispersion is prepared byadding to the resulting mixture, at 60° C., 8.75 grams of an aqueoussolution containing 75 percent by weight of lactic acid which isfollowed by the slow addition of 1397 grams of deionized water. Thisproduct is referred to as Resin Dispersion 3.

Resin Dispersion 3 is blended with 111 grams of Pigment Paste B to yielda cathodic electrodeposition paint having a pigment to binder ratio of0.2 to 1. Steel panels pretreated with zinc phosphate are cathodicallyelectrodeposited at various voltages for 2 minutes at a bath temperatureof 82° F. (27° C.). The wet films are baked at 275° F. (135° C.) for 30minutes. Film thicknesses are given in Table I.

EXAMPLE 4

A cationic electrodeposition resin is prepared by charging into asuitable reactor 247.5 grams of Epoxy Resin C, 371.2 grams of EpoxyResin D, and 381.3 grams of bisphenol A. The mixture is heated to 80° C.and 1.9 grams of a 70% solution of ethyltriphenylphosphoniumacetate.acetic acid complex is added. This blend is stirred whileheating at 1.5° C./minute to 150° C. whereupon it exotherms to 165° C.where the temperature is held for about one hour. The epoxy equivalentweight of the resulting resin is 1861.

To 175 grams of this advanced epoxy resin is added 19.4 grams ofpropylene glycol phenyl ether solvent at 120° C. This resin solution iscooled to 70° C. and a solution of 8.37 grams of dimethylethanolamine,8.05 grams of an aqueous solution of 72.5% lactic acid, and 42.3 gramsof water is added dropwise. The reaction mixture exotherms to 80° C. andthe temperature is controlled at 80° C. for six hours.

To the reaction product at 80° C. is added 2.64 grams of dibutyl tindilaurate catalyst and 189 grams of Curing Agent B.

While agitating continuously, a cationic dispersion is prepared byadding dropwise to the resulting mixture, at 70° C., 1702 grams ofdeionized water. This is Resin Dispersion 4.

Resin Dispersion 4 is blended with sufficient Pigment Paste B to yield acathodic electrodeposition paint having a pigment to binder ratio of 0.2to 1. Steel panels pretreated with zinc phosphate are cathodicallyelectrocoated at various voltages for two minutes at a bath temperatureof 80° F. (27° C.). The wet films are baked at 350° F. (177° C.) for 30minutes. The resultant film thicknesses are shown in Table I.

COMPARATIVE EXPERIMENT A

A cationic electrodeposition resin is prepared by charging into asuitable reactor 596.2 grams of Epoxy Resin D and 303.8 grams ofbisphenol A. The mixture is heated to 80° C. and 1.57 grams of a 70%solution of ethyltriphenylphosphonium acetate.acetic acid complex isadded. This blend is stirred while heating at 1.5° C./minute to 150° C.whereupon it exotherms and the peak exotherm is controlled below 190° C.by cooling. The temperature is then allowed to fall to 175° C. and thenmaintained at 175° C. until 70 minutes past the peak exotherm. The epoxyequivalent weight of the resulting resin is 1810.

To 313.1 grams of this advanced epoxy resin is added 78.3 grams ofethylene glycol monobutyl ether solvent at 120° C. This resin solutionis heated under nitrogen to between 110° C. to 130° C. and stirred toform a solution. The solution is then cooled to 80° C. and a mixture of15.9 grams of nicotinamide, 14.8 grams of an aqueous solution of 72.5%lactic acid, and 33.3 grams of water is added over a period of 30minutes to produce an opaque, whitish, viscous mixture. The reactiontemperature of 80° C. is maintained for 5.25 hours.

Thirty minutes after completion of the above addition, 44.6 grams ofadditional water is added over a period of 30 minutes. The reactionmixture is maintained at 80° C. for three hours after completion of thefirst addition. The product is a clear, light yellow, highly viscoussolution.

To 194.5 grams of the above product at 70° C. is added 3.3 grams ofdibutyl tin dilaurate and 118.2 grams of Curing Agent A. The mixture iscooled to 60° C. and 1185.0 grams of deionized water is added dropwise.The temperature of the mixture is steadily decreased as the additionproceeds such that the temperature is 40° C. to 50° C. when the mixtureinverts. This is Resin Dispersion 5.

Resin Dispersion 5 is blended with sufficient Pigment Paste A to yield acathodic electrodeposition paint having a pigment to binder ratio of 0.2to 1. Steel panels pretreated with zinc phosphate are cathodicallyelectrocoated at various voltages for two minutes at a bath temperatureof 80° F. (27° C.). The wet films are baked at 275° F. (135° C.) for 30minutes. The resultant film thicknesses are shown in Table I.

In electrodeposition coatings, higher voltages typically result inhigher film thicknesses. The data in Table I shows that even at highervoltages, the coatings of the prior art do not achieve the coatingthickness obtained by the present invention at lower voltages.

                                      TABLE I                                     __________________________________________________________________________            FILM    FILM    FILM    FILM    FILM                                          THICKNESS                                                                             THICKNESS                                                                             THICKNESS                                                                             THICKNESS                                                                             THICKNESS                                     IN MILS/MM                                                                            IN MILS/MM                                                                            IN MILS/MM                                                                            IN MILS/MM                                                                            IN MILS/MM                                    AT      AT      AT      AT      AT                                            INDICATED                                                                             INDICATED                                                                             INDICATED                                                                             INDICATED                                                                             INDICATED                             RESIN   VOLTAGE VOLTAGE VOLTAGE VOLTAGE VOLTAGE                               DISPERSION                                                                            50V 75V 100V                                                                              125V                                                                              175V                                                                              200V                                                                              225V                                                                              250V                                                                              300V                                  __________________________________________________________________________    1       --  0.73/                                                                             0.91/                                                                              1.0/                                                                             --  --  --  --  --                                                0.019                                                                             0.023                                                                             0.025                                                     2       --  0.47/                                                                             0.68/                                                                             0.83/                                                                             --  --  --  --  --                                                0.012                                                                             0.017                                                                             0.021                                                     3       0.55/                                                                             0.72/                                                                             0.82/                                                                             --  --  --  --  --  --                                            0.014                                                                             0.018                                                                             0.021                                                         4       --  --  --  --  0.62/                                                                             0.79/                                                                             1.0/                                                                               1.2/                                                                             --                                                            0.016                                                                             0.020                                                                             0.025                                                                             0.030                                      5*     --  --  --  --  --  0.35/                                                                             --  0.35/                                                                             0.4/                                                              0.009   0.009                                                                             0.010                                 __________________________________________________________________________     *Not an Example of the Present Invention                                 

What is claimed is:
 1. In a process of coating a cationic, epoxyresin-based composition onto an object having an electroconductivesurface by steps comprising immersing the electroconductive object intoa coating bath comprising an aqueous dispersion of cationic particles ofthe epoxy-based composition, passing an electric current through saidbath sufficient to electrodeposit a coating of said composition on theobject by providing a difference of electrical potential between theobject and an electrode that is (a) spaced apart from said object (b) inelectrical contact with said bath and (c) electrically positive inrelation to said object, the improvement which comprises using as thecationic resin composition a composition comprising a cationic, advancedepoxy-based resin having a charge density of from about 0.2 to about 0.6milliequivalent of cationic charge per gram of resin obtained byreacting in the presence of a suitable catalyst(A) a compositioncomprising(1) at least one diglycidylether of an aliphatic diol whichdiol is essentially free of ether oxygen atoms, and (2) adiglycidylether of a dihydric phenol, with (B) at least one dihydricphenol; wherein (A-1) and (A-2) are employed in such quantities thatabout 10 to about 75 percent of the diglycidylethers contained incomponent (A) are contributed by (A-1) and from about 25 percent toabout 90 percent of the diglycidylethers are contributed by (A-2), andcomponents (A) and (B) are employed in such quantities that theresultant epoxide equivalent weight is from about 350 to about 10,000;whereby, there is formed an advanced epoxy resin having terminal oxiranegroups and converting at least some of the oxirane groups to cationicgroups.
 2. The process of claim 1 in which the amount of diglycidyletherof an aliphatic diol in the resin is from about 10 percent to about 50percent.
 3. The process of claim 2 wherein a capping agent, component(C), is combined with components (A) and (B) of the resin in an amountof from about 1 percent to about 15 percent based on the total weight ofdiglycidylethers in the cationic, advanced epoxy based resin.
 4. Theprocess of claim 3 in which the amount of diglycidylether of analiphatic diol in the resin is from about 15 percent to about 35percent.
 5. The process of claim 1, 2, 3 or 4 in which the coating bathalso contains a curing agent.
 6. The process of claim 5 in which thecuring agent is selected from a blocked polyisocyanate, an aminealdehyde resin, and a phenol aldehyde resin.
 7. The process of claim 6in which the curing agent is a ketoxime-blocked polyisocyanate.
 8. Theprocess of claim 5 in which the coating bath also contains a pigment. 9.The process of claim 6 in which the coating bath also contains apigment.
 10. The process of claim 7 in which the coating bath alsocontains a pigment.